The present invention relates to a toggle lever clamping unit for an injection moulding machine.
A toggle lever clamping unit generally comprises a fixed platen, a movable platen and a support plate. Between the support plate and the movable platen, a toggle lever mechanism is arranged, which can be actuated by means of a drive device. The toggle lever mechanism consists of a plurality of levers connected articulatedly to one another, which are connected by articulations to the support plate and to the movable platen. In order to be able to actuate the toggle lever mechanism between a swung-in position of the levers and a swung-out position of the levers—also designated extended or dead centre position of the toggle lever mechanism—, the drive device is operatively connected to a cross clamp or to a plate, which fulfils a similar function, which in turn is articulatedly operatively connected to one or more levers of the toggle lever mechanism. The drive device serves for the opening and closing of the toggle lever clamping unit and is also to be configured for the application of the clamping force. The two operating phases of opening and closing on the one hand, and of the application of the clamping force on the other hand, differ here considerably in their requirement profile. On opening and closing, the movable platen is to be moved as quickly as possible, wherein only the mass moments of inertia and frictions have to be overcome. This travel movement often also takes place over a longer path. On application of the clamping force, the actuation elements realize a path, but this acts as a force on the plates which are touching each other. The path covered on application of the clamping force is necessary, in order to compensate for the elastic expansion of the components under clamping force. Enormous clamping forces are to be applied, in order to be able to press the halves of an injection moulding tool with the required force and to keep them shut. For application of the clamping forces, the stroke of the toggle lever, or a separate drive, installed independently of the cross clamp, can be used.
Various types of toggle lever clamping units are known from the prior art, in which at least a substantial portion of the opening and closing actuation is brought about by means of an electric motor. Here, the electric motor serves in particular to open and to close the clamping unit, which it can bring about in an energy-efficient and rapid manner. The electric motor can also serve to apply at least a portion, possibly a majority, of the clamping force. In addition to the electric motor, however, separate hydraulic drives can also be provided. Simple and commercially available piston cylinder systems can be used for the hydraulic drive. These piston cylinder systems can also be configured so as to be double-acting, so that they can be used on the one hand for applying the clamping force, but on the other hand can also be used in a supporting manner for pulling open the clamping unit at the start of the opening process. The hydraulic cylinder of such a piston cylinder system can be connected to a hydraulic supply via a simple valve. This valve can be a simple shift valve, which can optionally act upon the double-acting piston in both direction, or can set it ‘to idle’. With such an idle position, the piston would be able to be pushed freely to and fro.
A toggle lever clamping unit of the above-mentioned type is known from JP2010234584A, wherein an electric motor is provided for moving the cross clamp, and the additional hydraulic drive is formed by piston cylinder systems which are arranged between the movable platen and the fixed platen. The hydraulic cylinder of the piston cylinder system is fastened here to the fixed platen, and the piston rod of the piston cylinder system is fastened to the movable platen.
A further toggle lever clamping unit of the above-mentioned type is described schematically in WO2011003694A1, wherein an electric motor is provided for moving the cross clamp and wherein in different embodiments the main levers can be brought by means of hydraulic additional drives into the extended or respectively dead centre position. These additional drives are arranged between the cross clamp on the one hand and the main levers, on the other hand, arranged symmetrically on both sides of the central axis and acting between the support plate and the movable platen. In a first embodiment, hydraulic cylinders are provided in or on the cross clamp. The associated piston rods are operatively connected respectively to a connecting lever mounted on a main lever. In a further embodiment, the connecting levers are formed between the cross clamp and the main lever itself as a piston cylinder system. Here, for example, the cylinder can be mounted articulatedly on one of the main levers and the piston rod can be operatively connected articulatedly with the cross clamp.
EP2456607B1 discloses diagrammatically a further toggle lever clamping unit with an electric motor for moving the cross clamp and with hydraulic additional drives, in order to be able to bring the main levers into the extended or respectively dead centre position. In some embodiments, the hydraulic additional drive is arranged between the support plate and the main levers which are connected to the support plate. In other embodiments, the hydraulic additional drive is arranged between the movable platen and the main levers, which are connected to the movable platen. When the hydraulic additional drive is connected to the main levers, with a horizontal position of the drive the operating direction is unfavourable for the power direction. The transferable energy is small; at the same time, the design of the structure must be correspondingly stable. When the hydraulic additional drive lies vertically, the geometric arrangement is critical, because the installation space is limited. A further embodiment provides the arrangement of hydraulic additional drives between two main levers, lying opposite one another and mounted on the movable platen. It remains unconsidered, that the main levers swing in strongly in the direction of the central axis on their movement into the open position of the clamping unit, so that a practical implementation may be difficult.
From JPH10258451A a toggle lever clamping unit is known, in which an additional movable auxiliary plate is provided between the movable platen and the support plate. In this auxiliary plate, a hydraulic cylinder is integrated, the piston of which is connected to a piston rod, which is directed out from the auxiliary plate and is operatively connected to the movable platen. The electrically driven toggle lever mechanism is operatively connected by drive technology to the support plate and to the auxiliary plate.